1. Field of the Invention
This invention relates generally to a new composition of matter and, more specifically, to a new high oxidation state metal-oxo catalyst which can be used for generating hydrogen from water, in one embodiment the high oxidation state metal being molybdenum.
2. Brief Description of the Related Art
Owing to issues of climate change and accelerating global energy demands, the search for viable carbon-neutral sources of renewable energy is amongst the foremost challenges in science today. One such alternative is hydrogen, which can potentially be used as a clean replacement for fossil fuels in many applications, including transportation in cars, buses, trucks, trains, and airplanes. It can further be used in fuel cells for powering mobile devices such as lap-top computers and cell phones, as well as for meeting power requirements in buildings and industry. Many industries also use hydrogen as a reactant. One example is the Haber-Bosch process that produces ammonia, which currently relies on steam reforming of natural gas or liquefied petroleum for the production of hydrogen. This is expensive, environmentally unsustainable (based on finite resources of fossil fuel and produces carbon dioxide and hydrogen sulfide, two major atmospheric pollutants) and necessitates removal of sulfur which deactivates the catalyst used for ammonia production. Hydrogen is also used as a reducing agent for metal ores, for the production of hydrochloric acid and as a hydrogenating agent for unsaturated fats and oils.
In this context, where hydrogen has emerged as an attractive candidate for a clean, sustainable fuel as well as a precursor to many essential compounds, an intense interest in creating artificial systems that utilize earth-abundant catalysts for efficient hydrogen production from water has developed. A major quest of this renewable energy research is the search for efficient catalysts for the production of hydrogen from water, which rely on cheap, earth-abundant elements.
Hydrogenase enzymes possessing earth-abundant iron and/or nickel cofactors have been found to catalytically evolve H2 from neutral aqueous solution at its thermodynamic potential, with turnover frequencies of 100-10,000 mol H2/mol catalyst per second. However, the large size and relative instability of these enzymes under aerobic, ambient conditions has led to the search for well-defined molecular complexes outside the biological milieu that can produce H2 from water. Although many examples of air- and moisture-sensitive synthetic iron-sulfur clusters have provided insight into hydrogenase structure and reactivity, they catalyze proton reduction from acids in organic solvents at fairly negative potentials of −0.9 to −1.8 V vs. SHE (the Standard Hydrogen Electrode). Metal complexes that evolve H2 at more positive potentials still require organic acids, additives, and/or solvents. As such, the creation of earth-abundant molecular systems that produce H2 from water with high catalytic activity and stability remains a significant basic scientific challenge.